Nails are skin appendages made by horny, hard tissue, a material derived from dead corneocytes and composed by keratin, a protein rich of sulphated aminoacids and S-S bonds. Nails grow in a pocket-life invagination of the epidermis, just under the cuticle on the dorsal surface of the distal ends of fingers and toes. The formation of the nail material for the nail plate is performed primarily as an extrusion from a nail matrix, a specialized tissue which occupies the lower portion of the nail pocket from its proximal end up the lunula. The most proximal component of the matrix provides the corneocytes of the dorsal nail surface. These usually provide a shiny surface. When the matrix is altered by disease or the nail surface is subject to trauma, this shine is lost. The nail matrix region is near to the nail bed, with which the nail plate strongly adheres up to the hyponychium. This last is the dorsal region of the epidermis lying between the nail bed and finger pad.
The growth rate of the nail plate, such as the increase in length beyond its free edge, depends on the extent of regeneration of nail cells in the nail matrix. The cell material formed there differentiates into plate-like horny structures which are passively pushed in the distal direction. The nail grows continually during the entire life of the organism, the growth rate decreasing with old age, and in certain conditions like impaired peripheral circulation, nail infection, psoriasis and other illnesses. Changes in the fingernails of old people are mostly related to diminished tissue repair and inflammatory or degenerative changes of the distal interphalangeal joint. These influences are associated with reduced rate of longitudinal nail growth, thinning of the nail plate and accentuation of longitudinal ridges.
Variations in thickness and consistency of the toenails occur in elderly and are mostly attributable to changes in peripheral circulation. Healthy looking nails should be smooth, curved, void of any spotting, and should not have any hollows or ridges. Nails in bad conditions can be very harmful for the personal image, if neglected can cause chronic infections, associated to long-lasting embarrassment and pain. Noteworthy, they may be considered a social problem and/or a professional illness. Since fingernails especially, but also toenails, are in constant contact with the environment, they are subjected to a great deal of minor and sometimes major trauma.
The average monthly increase in length of the fingernails is between 1-3 mm, and, in addition to age, circulation and specific illnesses, diet and physiological stresses can influence this value. The nails of the dominant hand are reported to grow faster. Toenails grow significantly more slowly than fingernails, thus while 6 months are needed by a thumb nail to complete re-growth, at least 12 months are needed by a big toenail, or by the other toenails, for their complete re-growth.
Nail growth plays a precise role in the treatment of onychomycosis and of other nail illnesses, as the complete re-growth of a healthy nail is part of the primary endpoint of each therapeutic protocol: thus, factors that can increase nail growth rate may have a decisive role in shortening the treatments of nail illnesses.
Chitosan derivatives, such as hydroxyalkyl chitosans and/or carboxyalkyl chitosans, are known in the art as water-soluble film forming agent. Their use is for instance disclosed in EP1303249, which discloses a nail varnish composition containing at least one antimycotic agent, and in WO2004/112814, which discloses a nail restructuring composition based on one herb extract from the genus Equisetum in combination with hydroxypropylchitosan, which is used as a film forming agent. The use of chitosans as film forming agents is also disclosed in WO2006111426 and in WO2007042682; the use of chitosans is also disclosed in Wenk, Myfungar Nagellak, Haut, Viavital Verlag, Essen, DE, Vol. 15, n. 7, 2004, pages 307-308; RU2108114; EP10679383; Monti et al., Drug Development and Industrial Pharmacy, 2005, United States, vol. 31, n. 1, 2005, pages 11-17; WO03051376.
It has now been found that the growth of nails may be accelerated by the application of products containing chitosan or chitosan derivatives, either alone or in combination with one or more active principles, on the nail plates.